Probing the core-mantle boundary beneath Europe and Western Eurasia: A detailed study using PcP

摘要: Summary We use PcP (the core reflected P phase) recordings of deep earthquakes and nuclear explosions from the Grafenberg (Germany) NORSAR (Norway) arrays to investigate core–mantle boundary region beneath Europe western Eurasia. find evidence for a previously unknown ultra-low velocity zone 600 km south-east Moscow, located at edge middle-size low shear- imaged in seismic tomography that is Volga river region. The observed amplitude variations can be modelled by reductions S-waves −5% −15%, respectively, with density increase +15%. Travel time delays pre-and postcursors are indicating thickness about 13 km this (ULVZ). However, our modelling also reveals highly ambiguous reflection off top anomaly various ULVZs topography models. Accordingly, large contrasts up −10% VP −20% VS cannot excluded. In general, whole shows complex pattern amplitudes caused most likely CMB undulations. Further probes Paris, Kiev northern Italy indicate normal conditions, whereas samples below Finland Hungary–Slovakia border yield strongly amplified signals suggesting strong effects. evaluate behaviour as function distance several ULVZ models using 1D reflectivity 2D Gauss beam method. influence perturbations analysed well thickness, dominant period source wavelet interface topographies. Strong variation obtained impedance contrast. consider two types topographies: undulations atop presence flat vice versa. Where broad range dimensions lead variations, only generate significant scattering. Consequently, indicates effects anomalies may mask true medium parameters thickness. Moreover, there might possibility misinterpreting precursor PcP, particular thin ULVZs.